1. Field of the Invention
The present invention relates to an image forming apparatus provided with an electric power saving mode for suppressing an electric power consumption.
2. Description of the Related Art
There is known an electrophotographic image forming apparatus equipped with an electric power saving mode for suppressing an electric power consumption by keeping a fixing device for thermally fixing a toner image on a recording sheet (hereinafter, simply called as “a sheet” or “sheets) in a standby state by lowering the temperature of the fixing device to a predetermined temperature, if an image formation is not performed for a predetermined period. An example of the image forming apparatus equipped with the electric power saving mode is e.g. disclosed in Japanese Unexamined Patent Publication No. 2004-230605.
Specifically, the apparatus disclosed in the publication is constructed in such a manner that a storage stores therein the number of times when the apparatus performs a printing operation without shifting to the electric power saving mode after the power source of the apparatus is turned on, and the number of times when the apparatus shifts to the electric power saving mode without performing a printing operation after the power source of the apparatus is turned on. If the number of times when the apparatus performs a printing operation without shifting to the electric power saving mode after the power source of the apparatus is turned on is larger, a warm-up operation is performed, in other words, the temperature of the fixing device is swiftly increased to a predetermined fixing temperature necessary for fixing a toner image on a sheet immediately after the power source of the apparatus is turned on. If, on the other hand, the number of times when the apparatus shifts to the electric power saving mode without performing a printing operation after the power source of the apparatus is turned on is larger, the apparatus is swiftly shifted to the electric power saving mode immediately after the power source of the apparatus is turned on to thereby suppress an electric power consumption.
There is also known an arrangement, in which it is determined whether the apparatus is to be shifted to the electric power saving mode next time, or a warm-up operation is to be performed, when the power source is turned on before the power source of the apparatus is turned off.
The following drawback is involved in the arrangement in which it is determined whether the apparatus is to be shifted to the electric power saving mode, or a warm-up operation is to be performed next when the power source is turned on depending on a proceeding status of the apparatus to the electric power saving mode after the power source of the apparatus is turned on; or the arrangement in which it is determined whether the apparatus is to be shifted to the electric power saving mode, or a warm-up operation is to be performed next time when the power source is turned on before the power source of the apparatus is turned off. In some cases, the apparatus may be shifted to the electric power saving mode against a user's intension to start printing immediately after the power source of the apparatus is turned on, or it may take an unduly long time until the apparatus is brought to a printing ready state. In other cases, a warm-up operation may be started against a user's intension to save an electric power consumption after the power source of the apparatus is turned on, which may resultantly increase an electric power consumption.